Structures and negative thermal expansion properties of solid solutions YxNd2−xW3O12 (x = 0.0–1.0, 1.6–2.0)

A new series of rare earth solid solutions of YxNd2−xW3O12 (x = 0.0–1.0, 1.6–2.0) were successfully synthesized by the solid-state method and studied by X-ray and neutron powder diffractions. The samples were found to crystallize in monoclinic with space group C2/c for x = 0.0–1.0 and in orthorhombic with space group Pnca for x = 1.6–2.0. Thermal properties of YxNd2−xW3O12 (x = 0.25 and 1.90) were studied with high-temperature XRD. It was found that the thermal behaviors of YxNd2−xW3O12 depend not only strongly on their structures, but also on their compositions. Positive thermal expansions of compound Y0.25Nd1.75W3O12 are found to be anisotropic along the three crystallographic axis, where a-axis expands in the 25–200 °C range but contracts in the 200–800 °C range, while b- and c-axes show expansion in the whole temperature range. Negative thermal expansion coefficient of Y1.9Nd0.1W3O12 was calculated to be −17.9 × 10−6 K−1 from 200 to 1000 °C, comparing to −20.9 × 10−6 K−1 of Y2W3O12.